A Closer Look at Stealth, Part 5: Nozzles and Exhausts

F-117 Nighthawk

The F-117A Nighthawk was the first U.S. aircraft to use low-observability as its primary means of survivability. The rear of the aircraft sloped from an apex above the cockpit into a broad, flat feature dubbed the “platypus.” The engine exhaust flattened to thin slots 4-6-in. deep and 5-ft. wide, divided horizontally into about a dozen channels. The lower fuselage terminated in a lip extending 8 in. past the exhaust at a slightly upward angle. This was covered in “heat-reflecting” tiles that were cooled by bypass air from the engines. The platypus shielded the hot metal parts while the flattened plume reduced IR intensity from the side and accelerated mixing with ambient air. The extended lip masked the exhaust slot and first 8 in. of plume from below, while the low-emissivity tiles limited IR absorption and emission.

B-2

Buried deep within its flying-wing airframe, the B-2’s engines are prevented from heating the outer surface. The exhaust is cooled by bypass air, including from secondary air intakes, and flattened prior to exiting over the “aft deck”—trenches built of titanium and covered in low-emissivity ceramic tiles. Likely containing magnetic radar-absorbent material (RAM), these extend several feet behind the nozzles, blocking the plume’s core from below and the side. Large chevrons at the end of the engine fairings and aft deck also introduce shed vortices to accelerate mixing with ambient air.

F-22 Raptor

Pratt & Whitney incorporated a number of IR signature-suppression techniques into the F119 engines that power Lockheed Martin’s F-22 Raptor. Aft of the low-pressure turbine are thick, curved vanes that, when looking up the tailpipe, block any direct view of the hot, rotating turbine components. Fuel injectors are integrated into these vanes, replacing the conventional afterburner spray bars and flame holders. The vanes mask the turbine and contain minute holes that introduce cooler air. The exhaust then passes through the F119’s “non-axisymmetric,” or 2D, thrust-vectoring nozzles, which have upper and lower surfaces ending in wedges with blended central edges. These nozzles further mask the engine hot parts while flattening the exhaust plume and generating vortices. Minute holes are evident on their inner surfaces, likely providing bypass air for enhanced cooling.

F135 Engine

In designing the nozzle of the F135 engine that powers the F-35 Joint Strike Fighter, Pratt & Whitney aimed to rival the low signature of the nozzles on its previous F119, while beating it on maintenance costs. The F135 nozzle comprises two overlapping sets of 15 flaps, offset so outer flaps are centered on the gaps between the inner flaps. The inner flaps are thin, have metallic exteriors and straight sides and terminate in inverted “V”s. The sides create rectangular gaps between them with the nozzle fully diverged. The outer flaps, which Pratt calls “tail feathers,” are thicker and covered in tiles with blended facets. They terminate in chevrons that overlap the ends of the inner flaps to create a sawtooth edge. Toward the fuselage, the tiles end in four chevrons and are covered by additional tiles (not attached to the engines in this photo) that terminate fore and aft in chevrons and interlock with adjacent tiles in sawtooth-fashion.

The F135 nozzle likely suppresses IR signature using multiple methods. The trailing-edge chevrons create shed vortices, shortening the plume, while their steeper axial angle likely directs cooler ambient air into the exhaust flowpath. The inner surfaces of both sets of flaps are white and covered in minute holes similar to those on the F119, which might supply cooling air. The space between the tail feathers and the trailing chevrons may also contain ejectors to provide even more cooling air. The tiles and inner flap surfaces are likely composed of low-emissivity, RAM composites.

Improvements in infrared (IR) detection technology have made it possible for IR search-and-track systems and IR-guided missiles to acquire aircraft at increasingly long distances. The technology poses a growing threat to aircraft that only suppress their radar signatures. Therefore, in State of Stealth, Part 5, Aviation Week takes a deep dive into the IR side of low-observability. Among the most important factors in limiting an aircraft’s IR detectability is addressing the large signatures created by the engines’ hot part, nozzles and exhaust plumes. In this gallery, we examine the approaches to reducing engine and plume IR signatures that have been taken on the F-117, B-2, F-22 and F-35.

F-22, F-35, B-2, are all worthless just like the F-117 that was retired to Davis-Mothan AFB Boneyard back in November 2008. IRST and other types of Infrared systems can (Find, Fix, Track, Target and Engage) each of these platforms and shoot them down utilizing Ground to Air or Air-Air CONOPS.

The POTUS needs to FIRE all Air Force Senior Leadership and hire WARRIORS in the Ranks. We have been lied to for over 20 years and are spending Billions and Trillions based complete bogus information. The entire Senior Leadership at the DoD needs to be FIRED by the POTUS. POTUS needs to STOP all prior Admiral and Generals from being Lobbyist or providing Acquisition information to any prime integrator or information biases following retirement except without permission of the POTUS.
These Retired General officers promote their Friends then go to work for a Major Integrator (LMCO) then go back to lobby the people they promoted. This is absurd and exactly why Wall Street and Feds, Big Pharma and FDA, Healthcare and Insurance. A Joke.
STEALTH IS DEAD, IRST, S-400, S-400 and other advisory Radar and Infrared Tracking. We are setting ourselves up for defeat while spending TRILLIONS FOR NOTHING!!!!!!!!!!!!

The more exclamation marks you use, the less credibility you have. Screaming at the top of your lungs does not make anything you say more accurate or worth anyone's time to read it.

Sentences that actually make sense generally help, too. Because verbs.

Also, it would help if you actually read the photo captions, which describe anti-IR techniques on the very same aircraft you love to hate. Your rant about nothing is being done to counter IRST is somewhat undermined by that.

Mr. E, you are delusional about seeing our 5th gen. stealth! It just ain't happening -- Israel is proving it with the F-35 already against all the Russian junk in Syria. The US isn't flying the F-35 there yet, but the F-22 flies there with impunity despite the S-400's they claim to have there !

The gentleman has a point. We spend trillions on defense and we get missiles that can't hit anything including Patriot, THAAD and The alleged Ballistic Missile Defense System, and then we are dumb enought to deploy them, Stealth aircraft that are neither stealthy nor equipped to fight but we deploy them and a peanut sized country with no economy but with Chinese money...read that our money...finances them to build intercontinetal missiles designed to kill us and we hear how great our "relationship" is. Sometimes a rant has elements of truth that are worthy of consideration. If we don't get ourselves on track we are in for a world of hurt.

I presume user-2788752 that you are referring here to North Korea. Sadly this is not a problem that can be solved by military means as we, and the Chinese, are not dealing with a rational mindset but one which is prepared to take down the world with him. It is probable that at the first indication of an attack he would unleash a devastating blow on South Korea and possibly Southern China. At the end of WW2 when the Russians were poised for the Battle for Berlin, Hitler was pressed by a number of generals to surrender the city and save the lives of thousands of German civilians. Hitler's reply was that those Germans that were not prepared to die for the glory of the Third Reich were not worthy of being called Germans and deserved to die. That is the mindset we have to deal with in North Korea. North Korea is as big a problem to the Chinese as it is to Japan, Russia, South Korea and the USA and the only way we will get a solution is by the cooperation of all four Governments working towards a diplomatic solution. Nothing else will work.

Russia is blocking any movement in the UN because the crazy fat boy is trying to poke us in they eye.

And saying that there is not a military solution is not correct, even remotely. Half measures will not work but NK couldn't last a week on its own. What is sad is that China would probably back them again and make it far messier than it needs to be...but we should call them on it this time and make them pay for their misdeeds not just let them create yet another UN backed stalemate for decades allowing the despots to flourish.

Thorulf, Your State Department has stated that there is no Military solution to the problem of NK and that you are going to have to find a diplomatic solution. Russia is blocking further sanctions on the rational grounds that "they just don't work". China is just as worried about NK as the rest of the world as a military adventure would result in millions of refugees flooding across the Yalu river into Southern China. If we look at the effects of Military adventures the US and to some extent the UK have become involved with Vietnam, Afghanistan and Iraq don't stand out as howling successes.

By the way the Fat Boy is trying to poke everybody in the eye, he's a loony, its just that the present incumbent of the White House is the easiest target around and gives the most satisfying response to the Fat Boy's eye poking. Read up on psychology and you will see how it works.

The Israeli designed and 50% US funded Arrow III, Magic Wand and Iron Dome all WORK and combat tested. They work because the US Patriots failed in 1991 against Saddam's Scuds. Israel needed ABM systems that actually worked and at a fraction of US prices. And developed them. The US funded 50% of those Israeli designs and is a partner that gives the US (1) the right to use much of their technologies, and (2) gives the US a veto on to whom they can be sold. But affordable, accurate and combat tested ABM systems exist! Will we use them in place of more expensive and less accurate US made systems? I doubt it. But affordable antidotes to ICBMs exist! But our brass hats seeking jobs later on will always choose the US made stuff not matter how much more they cost, or how much less effective they may be.

Yeah, all that BS must be the reason why Israelis buy their equipment from the US, right? And why Israeli systems back in 1991 were NOT able to defend against Scuds because they didn't have anything, which is why Patriots were there... And the Israelis have a ship-based MDS right?.. Or the ability like our GBI to intercept LONG-ranged ICBMs at high altitudes, right?

Although E.Wolkerstorfer makes his arguments in a more "shouty" manner than is probably necessary he is in essence correct. There are three facts of life that need to be taken into consideration:-

1. Stealth reduces radar reflectivity, it does not eliminate it.

2. Any jet aeroplane is going to be followed by a significant hot gas plume.

3. Radars and infra-red sensors now employ computer software which enables them to detect extraordinarily weaker returns than could be detected by human operators watching a screen.

Astronomers are now detecting planets moving across stars several light years away by having the computer detect the minuscule reduction in light intensity as the planet crosses in front of the star. NASA is using radar to detect individual asteroids several million miles from earth. In both these cases it is a computer program that enables the detection of the planets and asteroids.

There is also the fact that computer systems are getting smaller and more powerful on an almost continuous basis. Google "Moores Law". and this means that both weapon and detection systems are getting smaller, cheaper and more powerful all the time.

Does it make sense to build a $100,000,000 attack aeroplane, that can be taken out by a $10,000 shoulder launched missile.

sdp, that's the easy bit. Firstly, a defence system does not have to monitor half a million cubic miles of air but only the area that would contain the probable threat. Secondly, electronics are now getting so small and powerful that very effective sensors can be built into lots of early warning aeroplanes that can act as "picket ships" in time of threat. We are not talking here about an ICBM strike but an attack by conventional jet aeroplanes such as the F-35 which will be operating at sub-sonic speeds for most of the sortie. If you link these to a flying armoury with a large number of long range air to air missiles then the F-35's probably wont ever reach the target area. The Royal Air Force toyed with this idea in the 1960's and had a study done on using the Vulcan as the flying armoury. The whole idea was shot down by the fighter pilot's trade union.

None of us commenting on this board has access to the highly classified data on the effectiveness of measures to detect stealth aircraft. If we did, we shouldn't be commenting.

That said, we know that all the technologically advanced nations --- the US, Russia, China, UK, France, Japan, Germany, etc -- have doubtless done considerable research on the likely future effectiveness of stealth. And ALL of these countries -- except maybe France -- are either developing stealthy aircraft or buying stealthy aircraft from other countries.

The fact that these countries are all buying or developing stealthy aircraft tells us very clearly that their experts expect stealthy aircraft to remain very difficult to detect during the foreseeable future at useful combat ranges.

Also, MANPADS (shoulder launched missiles) almost never take out jets although they are useful against helicopters. And the F-35 won't be doing close air support within the limited vertical range of shoulder launched missiles.

Most sensible post in the thread. Those in the know of cutting edge stealth multi-discipline research are very small communities indeed and are not commenting on a public forum about it. I am sure they are doing their best to keep our 25 year lead in this realm.

Well stated WJLAviator. But organizational shortcomings within the USAF mentioned previously have enabled the monopolistic, long lead time environment that is the root of a lot of the problems plaguing major weapons programs.

The key differentiators here are of course operating band and array density/processing vs. he _expected profile_ of stealth operations.
In the 1970s, Russian IRST under the nose of their MiG-23/25 was little more than a missile seeker with permanet cooling loop using lead sulphide detectors with operating band in the 1-1.5u spectrum. Technology similar to that introduced on the F-8 and F-104 and later 'perfected' with the F-106, it could cue the weapons system only with help from the radar was largely an anti-jamming aid for aligning weapons seekers on very fine bearing lines.
Until you used burner. And then it could spot you from not ~10nm but closer to 40-50nm. Testing in support of the ATF program, using the TAC Brawler complex environment simulator showed generic ATF models could get hits from surveillance radars (longwave, Tall King etc.) about 30-40% of the time, just by 'beaming' them to provide a significant RCS bloom. Plug in the burner and the threat responded every time. Which can be useful if you are employing drag and coat trail tactics to draw CAPs off station to provide safe passage for interdictors or in front of other shooters.
Conversely, modern IRST are using 3-5u, midwave, technology which sees differently with much better cooling in the dewar an on photoplane preprocessing to keep quantum noise to down across arrays that are measured in the low hundreds rather than low tens of detector 'pixels'. Thus, IR-OTIS, the precursor to the Skywards-G now going into service on the JAS-39E/F, could detect targets farther than the PS-05 radar with a performance similar to that of the APG-73. At altitude.
The Russians, in their modern OLS-35/101 systems, coming into service on the Su-35 and T-50, are apparently moving towards longwave systems in the 10-14u bands, similar to the old TADS system on the AH-64 with similar 'hot body, not gas plume' detection in mind.
As anyone who has seen Youtube videos of either the F-22 or F-35 against the ramp or in flight diplay will have noted, the jets practically glow with internal heat, despite nominal measures to reduce _specific aspect_ heating with fuel-cooled leading edges and sophisticated heat exchange dumps into fuel headed for the engines. This, with midwave sensors (albeit at unnaturally close ranges) is astonishing.
Yet there are modifiers to be considered. The absolute size of a photoplane is currently in the 6-10" category. Getting good production yields with uniform detector performance, at cost, is simply not possible any higher, both due to effects on RCS from bigger apertures and due to cost. This means that the subtend area of coverage, even with SFPA technology (detector doped computer chips with DA processing on-pixel) is often less than a degree of coverage. While this makes for very high accuracy angle tracking, it also means that sweeping large arcs of sky results in HUGE volumes of sky which, due to high noise effects on target masking, simple anaprop as moisture absorption or failure to integrate snap-shot imaging frame data with a timing pulse (effectively passive video range gating) at the data level makes for sloppy coverage in the outer range areas.
Superb processing and manufacturng quality is thus everything in modern QWIP IRST and even then you can find conditions where moisture absorption takes 30nm off your detection window.
But stealth helps you out here. Becuase stealth is about altitude. Altitude to get legs on the jet. Altitude to give you sensor squint angles on ground targets which support SAR imaging. Altitude to give you best glide range. And altitude to take you above the weather bands which, in theory, can compromise VLO if the airframe is sheeted with enough ambient water.
Looking for a hot body, at altitude, in cold, dry, air solves a lot of an IRST's problems, IF it has the sensor orientation (top looks up, bottom, looks down) suited to it's own performance band.
In this, it is worth noting that the F-22s original EOSS was supposed to be a two aperture system, in the wingroots of the jet, with equal hemispheric coverage. That capability was later replaced by an RF apeture as part of the NCTR capabilities suite. The F-35 has an undernose EOTS system which is going to be all but worthless in an enviroment where it will continually be out-heighted due to it's inferior wingloading. And the Su-35/T-50 similarly have large blindspots in their 40K-20K look down coverage in the 20-25nm range zone where a solid IRST track could give them BVR dominance, even on a stealth jet.
Other (U.S.) systems like Tiger Eyes, FIRST-21 and Legion are all mounted in underbelly pod or scabbed sensor pylon positions which make them all but useless because the conventional F-15/16/18 either don't have the LO performance to be GBAD safe, at heights which guarantee threat look down from 20ft aft under the belly of the jet. Or/and are so lacking in aerodynamic capabilities of their own (specifically the Super Hornet) that they cannot fight at those FLs anyway.
IMO, the future of the system capability lies in it's employment _off airframe_, as part of a network sensor grid. Where 'location, location, location' is a regional mantra for EO systems performance, a range tracking camera sized aperture (10-20" minimum) will be highly expensive yet less so than the equivalent EWR it replaces, by perhaps 75%. (2-3 million vs. 10-12). The added detector area will theoretically allow multi-band color stacking to provide much more complex, blended, plume+body signature variance modeling to aid in long range detection while of course the look-up aspecting (and lack of passive-sensor threat) means a much increased airframe aspected area to look at, beyond what even fuel cooling can do to minimized pixels.
The alternative, is to retain fighter-sized installations but to mount them in VLO drones or LTAs/aerostats in such density that shooting them all down is impractical as a function of suppression while, in offense, they provide pre-raid arrival cues to threat exits from the baselanes if not WIW. It may well be that, as surveillance optimized systems with contrail diffusion chemicals, longspan wings, upperdeck inlets and thus _open ventral_ aperture allocations they will provide superior tracking coverage across the lower hemisphere, simply by using an articulated (EOTS type) sensor head as opposed to say DAS type multi-window patchworking of global visionics.
If the weather as CBase provides for it and/or you have sufficient performance to get above it, the prospects of opto-acoustic detection grids, using the full depth of a nation's territory to buy engagement window through handoff between trackfile composited EO systems must be considered a real vunerability of VLO systems in general and the speed/height/cooling limited F-35 in particular.

We need a Star Wars or Star Trek space kind of revolution to our civilian and military aircrafts, we need to invent new shaped technology for our near future aircraft, as we lost a lot of time till now trying to modify our already ailing old shape and design aircraft as even for the Stealth fighters and the new F35, which seems heavy in power plant with the mainframe and systems made design, engines are heavy and does not match the lift off powers as well as the G pull dog flight, it seems heavy for me as it is not for the F16 WHICH IS STILL THE KING OF THE SKY'S.

We may be missing the vital point here. First you have radar stealth and now IR avoidance. What will the do when they find their scopes littered with thousands of points with most of those points being drones (cheap version of the X47B) throwing out both radar and IR signals. Who do you shoot at? Your guess.

The shock diamonds in an afterburner exhaust apparently make good radar corner reflectors. Apparently this rather spoiled the RCS achieved in the A12/SR71, to the extent that they didn't bother with the radar absorbant wedges in the wing edges after the first few A12s.

Best laid plans of mice and men and all that. I guess it was the first time anyone has ever been motivated to make RCS measurements on an aircraft that could sustain afterburner for long periods of time. So it's not surprising that it caught them out. Still an awesome aircraft. I think they tried a fuel additive to reduce the effect.

Sometimes too much is given away in these articles...but then there must be a good reason? That said... the USAF in trying to convince mostly the technically ignorant public that they have a "good thing" in their arsenal. Actually in truth they are trying to convince themselves & the enemy that in combat "we are a formidable force Not to be reckoned with!"
Only in an actual combat situation will these aircraft prove their worth...then & only then! And let's hope it was worth the $$$$...tax payer's $$$$$!

It may be time to go back to before radar days. I think that during WW1 they detected airplanes by acoustic methods. Today autonomous microphones connected via computer network can easily triangulate positions of incoming enemy planes. same thing for shooting them down once you know approaximately where they are
direct the missile acoustically. Are these stealthies flying without noise?

The planes were a bit slower during WWI. Today they are fast enough that their noise does not precede them by very much. In the case of supersonic speeds, it doesn't precede them at all! Either way I doubt it would be possible to direct a missile accurately using acoustics.

Acoustic detection was used in WWII in Britain. It didn't get much use as the Chain Home radar system was far superior.

Modern jets are curiously quiet head on. I guess that's deliberate, but probably also easily achieved; the noisy exhaust is at the back.

You can determine the path of bullets, and the point of firing, using microphones to measure the shape of the supersonic shock wave. You could do the same thing with a supersonic aircraft and, assuming that it doesn't change course, get a missile on to that track pretty accurately.

POTUS needs to FIRE all Air Force and Navy Senior Leadership. He Needs to open an immediate investigate miss-representation, lack of design capability and Fraud Waste and Abuse against DoD and Lockheed Martin. These people need Federal Prison.

As previously stated. The F-117 was Shot Down during the Yugoslavian Campaign and Retired from the Air Force in November 2008. Stealth is Dead!! S-400 and S-500 and In farad Search and Track will identify destroy and "Stealth" platform. Russian and China received pieces of the F-117 along with numerous other weapons and they engineered radar and IR systems to kill any "Stealth Platform". Yet they Continue to lie to the American People. F-35, F-22, B-2 needs to cancelled ASAP by President. This is ridiculous.

Mr Workerstorfer's English in his repeated rantings is too good to be
Chinese, but perhaps acceptable for a Russian gentleman's comments.
I think, he would just like to "fire" or eliminate all of America, not just
its government. He certainly puts an interesting distraction to the topic.
More to the topic, at the beginning of WWII the British built up a radar
screen along the English Chanel to see the oncoming German Luftwaffe planes. The Germans tried to destroyed them, but it all evolved into the famous aerial battle over the English Chanel with
WWI style dogfights and terrible losses to both sides. Then came
the Battle of Britain, which was another "close encounter" battle resulting incredible losses to both sides. Then in 1943 started the
Allied's bombing campaign, and the Germans were able to watch
the "gathering eagles" over England as they assembled, yet once
they were away, the Luftwaffe often could not find them over Germany!
From then on it was again, if they bumped into each other, a close encounter, where no radar or chaff helped, just the guns and cannons.
Should I recount the Vietnam airway too, where extensive radar and
anti radar technology was deployed by both side? Losses were big there too.
My point? Putting all your eggs into one basket (stealth ?) is a very
risky decision for the long run. The lone F117 over Serbia was shot
down by a fast thinking Hungarian-Serbian electronic specialist, who
happened to figure out the right counter measure. For the West's sake
I hope that the F35 will produce all it is promised to. In an all out encounter we can run out of fighters and bombers very quickly.

Program Excellence Initiative

Gather, analyze, learn, apply.

Aviation Week’s annual Program Excellence Symposium unites leaders from across aerospace and defense companies, from program/project leaders and engineers to the IT experts, supply chain managers and strategic planning executives who together create performance success. This year’s program —to be held Oct. 23 in McLean, Virginia — will include:

Insight about the future of critical programs
Analyze where the industry stands in setting strategies for the near and long term
Three best practices that will improve your program performance today